Globally, malaria is the most important parasitic disease, affecting 300-500 million persons annually. Of the malaria cases (450,000 in 1996) reported in Brazil, 99 percent occurred in the Amazon region. In both 1995 and 1996 Roraima State in northern Amazonian Brazil had the dubious distinction of having the highest annual parasitic index (IPA) in Brazil. In Roraima, the principal anopheline malaria vectors have not yet been identified or incriminated, and virtually nothing is known about population structure, seasonal fluctuations or breeding site preferences. This basic biological information will ultimately be used to more effectively control local malaria transmission. Using molecular techniques, this project proposes to accurately identify the main malaria vectors, incriminate those responsible for transmission, and examine population structure and breeding sites within species of the Anopheles albitarsis complex and An. darlingi, both of which are present in the proposed study sites in Roraima State. Anopheles darlingi is the most efficient malaria vector in Latin America but species in the An. albitarsis complex (An. marajoara, in particular) have been implicated as important local vectors in nearby Amapa state in Brazil. These species are in the neotropical subgenus Nyssorhynchus. Adult and larval mosquitoes will be collected monthly in two endemic malaria sites (one rural, and one urban) near Boa Vista in Roraima State. Adults and larvae will be identified using either morphological keys (where they can accurately distinguish species) or newly developed molecular probes. Molecular identification of cryptic species will be coupled with parasite detection of ELISA. Microsatellites primers (recently developed for An. darlingi) will be used to compare population structure in larval breeding sites and adult collections in each of the two endemic collection sites.